Enhanced activity of nuclei for physical development



United States Patent 3,291,608 ENHANCED ACTIVITY OF NUCLEI FOR PHYSICALDEVELOPMENT Herbert S. Elins, Rochester, N.Y., assignor to Eastman KodakCompany, Rochester, N.Y., a corporation of New Jersey No Drawing. FiledFeb. 3, 1964, Ser. No. 342,267 11 Claims. (Cl. 96-66) This inventionrelates to physical development nuclei of enchanced activity and the useof these nuclei in preparing photographic products.

There are two basic methods for obtaining developed silver images, oneof which is chemical or direct development and the second method istermed physical development. By the latter method a physical developeris used containing a reducing agent, a soluble silver salt as a sourceof free silver ions, and other materials to adjust pH and silver ionconcentration. These solutions deposit silver upon nuclei which may bezinc sulfide, lead sulfide, nickel sulfide, silver selenide, colloidalgold, colloidal silver or the like. In a modified form of physicaldevelopment referred to as prefixation physical development the silverhalide is not dissolved out first but the developer solution contains astrong silver halide solvent such as sodium thiosulfate which dissolvesthe halide as development proceeds.

One object of my invention is to provide nuclei having enhanced activityin phyiscal development ope-rations. Another object of my invention isto provide a method of making zinc sulfides which are especially adaptedfor use in products intended for physical development. A further objectof my invention is to provide photographic products intended forphysical development in which sulfides of enhanced activity inaccordance with the in vention are employed. Other objects of myinvention will appear herein.

I have found that metallic physical developement nuclei prepared in thepresence of a chloranil-modified gelatin exhibit superior propertieswhen employed in physical development operations. The gelatin employedas the peptizing material in preparing these nuclei is formed by addingtetrach-loro-p-benzoquinone (chloranil) to an aque ous solution ofgelatin whereupon modification of the gelatin occurs. The thus modifiedgelatin is then employed as the peptizin-g material for various metallicphysical development nuclei.

The preparation of chloranil-m-odified gelatin may conveniently becarried out as follows: 250 grams of a 10% aqueous solution of bonegelatin was dissolved in 650 cc. of distilled water at 40 C. 5 grams oftetrachloorp benzoquinone was added to the gelatin solution and the masswas stirred for 4 hours at room temperature. The mass was filteredthereby giving a tunbid solution which was subjected to centrifuging.There was thus obtained a clear red gelatin solution which was decantedfrom the yellow residue present and the mass was made up with distilledwater to a total volume of 900 cc.

For nuclei in physical development operations metallic nuclei have beensuggested, some of which are more useful for this purpose than others.The following description of preparing zinc sulfide may be followed inthe making of other metallic physical development nuclei useful inphotographic products. The solution of chloranil-modified gelatinobtained as described above at 40 C. was mixed with a solution of 1.26grams anhydrous sodium sulfite in 74 cc. distilled water and then with2.65 cc. of 0.944 Normal Na s. Immediately after mixing in the sodiumsulfide a solution of 2.60 cc. of 0.99 Normal zinc nitrate in 270 cc. ofdistilled water was run into the mass while stirring over a period of 4minutes, 35 seconds. There was thus formed a sol of zinc sulfide3,291,608 Patented Dec. 13, 19664-amino-3-methyl-N-ethyl-N(beta-hydroxyethyl)aniline /2H SO -H O grams1.274 K PO -H O do 50.0 [Ag-H moles 1X 10- Distilled water to make 1000cc.

The pH was adjusted to 12.0 with 6 N H 1 The free silver ionconcentration was adjusted from a solution of Ag(S203)2E prepared fromAgCl and N-a2S20s-5H2O. The total silver ion concentration of thedeveloper was 5 10- moles/l.

It was found that by the use of zinc sulfide nuclei prepared inchlorani-l-modified gelatin more active centers for physical developmentresult than in the case of like products in which the zinc sulfide isprepared in an untreated gelatin.

The following example illustrates the use of colloidal zins sulfidenuclei prepared in accordance with the invention in photographicproducts including a silver halide photographic emulsion. A photographicproduct was obtained composed of a cellulose acetate support havingthere-on a layer of silver bromoiodide photographic emulsion coated at acoverage of mg. of silver and 230 mg. of gelatin per square foot, overwhich was applied a layer of colloidal zinc sulfide nuclei prepared inaccordance with the invention which layer contained 0.2 mg. of zincsulfide and 560 mg. of gelatin per square foot. The described productwas exposed in an Eastman 1B sensitometer for 1/100 of a second. It wasdeveloped in a developer having the following composition:

Water to make 1.0 liter.

The product was subsequently rinsed, fixed for 2 minutes in a hypofixing bath, washed and dried. It was found that a low constrastnegative image was obtained in the exposed areas and a positive imagewas obtained in the unexposed areas which had considerably greaterdensity than that produced by the use of zinc sulfide nuclei prepared inuntreated gelatin. Greater differentiation was therefore obtainedbetween the contiguous negative and positive images when nucleidispersed in the chloranil-modified gelatin were utilized.

In other cases zinc sulfide nuclei were incorporated directly in silverhalide emulsion layers rather than in a separate layer. In those casesthe zinc sulfide prepared in chloranil-modified gelatin produced higherdensity positive images in the unexposed areas than were untreatedgelatin was employed. This is also true in products adapted for use insilver halide dilfusion transfer processes such as in the type describedin US. Patent No. 3,020,155 in that more active physical development wasobserved than is found where untreated gelatin is employed.

The invention although illustrated in connection with zinc sulfidenuclei is not restricted thereto. Other phys ical development nucleisuch as colloidal gold of silver, metallic sulfides, selenides ortellurides such as lead sulfide, nickel sulfide, colloidal silverselenide, colloidal silver telluride, or other metallic physicaldevelopment nuclei mentioned in the prior art as useful for this purposecan be prepared and used either as the sole development nuclei or mixedwith one another in accordance with the invention.

The colloidal metals may be prepared in the presence of achloranil-modi-fied gelatin by the dextrin reduction method ofpreparation of Carey-Lea as described in C01- loida-l Elements, byWeiser, John Wiley and Sons, New York, New York, 1933, page 119.Metallic as used herein refers to heavy metals and their salts such asare useful as physical development nuclei.

The invention has been described in considerable detail with particularreference to certain preferred embodiments thereof, but it will beunderstood that variations and modifications can be eifected within thespirit and scope of the invention as described hereinabove and asdefined in the appended claims.

I claim:

1. A composition useful in preparing photographic products whichcomprises chloranil-modified gelatin containing, dispersed therein,metallic physical development nuclei formed in situ.

2. A composition useful in preparing photographic products whichcomprises chloranil-modified gelatin containing, dispersed therein, zincsulfide physical development nuclei formed in situ.

3. A composition useful in preparing photographic products whichcomprises chloranil-modified gelatin containing, dispersed therein,clolloidal silver physical development nuclei formed in situ.

4. A method of preparing metallic physical develop ment nuclei whichcomprises preparing a dispersion in finely divided form resulting fromintroducing an aqueous soltution of zinc salt and an aqueous solution ofa water-soluble sulfide into an aqueous solution of chloranil-rnodifiedgelatin.

5. A product useful in reproduction procedures com prising a supporthaving thereon a layer containing a dispersion of metallic physicaldevelopment nuclei in chloranil-modified gelatin and wherein saiddispersion is obtained by preparing the metallic physical developmentnuclei in the chloranil-modified gelatin.

6. A product useful in reproduction procedures comprising a supporthaving thereon a llayer containing 'a dispersion of zinc sulfidephysical development nuclei in ghloranil-modified gelatin and whereinsaid dispersion obtained by preparing zinc sulfide in thechloranil-modified gelatin.

7. A product useful in reproduction procedures com prising a celluloseacetate support having thereon a layer containing a dispersion of zincsulfide physical development nuclei in chloranil-rnodified gelatin andwherein said dispersion is obtained 'by preparing zinc sulfide in thechloranil-modified gelatin.

8. A photographic material comprising a support having thereon a layerof a silver halide photographic emulsion and a layer containing metallicphysical development nuclei formed in situ inchloranil-rn-odifiedgelatin.

9. A photographic material comprising a support having thereon a layerof a silver halide photographic emulsion and a layer containing zincsulfide physical development nuclei in chloranil-modified gelatin andwherein said zinc sulfide physical development nuclei are obtained bypreparing zinc sulfide in the chloranil-modified gelatin.

1!). A photographic develop-ment process wherein a photographic materialcomprising a support having thereon a layer of a silver halidephotographic emulsion and a layer containing metallic physicaldevelopment nuclei formed in situ in chloranil-modified gelatin isexposed and developed by a physical photographic developer.

11. A photographic development process wherein a photographic materialcomprising a support having thereon a layer of a silver halidephotographic emulsion and a layer containing zinc sulfide physicaldevelopment nuclei in chloranil-rnodified gelatin and wherein said zincsulfide physical development nuclei are obtained by preparing zincsulfide in the chloranil-rnodified gelatin is exposed and developed by aphysical photographic developer.

References Cited by the Examiner UNITED STATES PATENTS Re. 25,88510/1965 Yackel et al. 96--76 X 2/ 1962 Yackel et al. 96-76 X OTHERREFERENCES NORMAN G. TORCHIN, Primary Examiner.

- C. E. DAVIS, Assistant Examiner.

10. A PHOTOGRAPHIC DEVELOPMENT PROCESS WHEREIN A PHOTOGRAPHIC MATERIALCOMPRISING A SUPPORT HAVING THEREON A LAYER OF A SILVER HALIDEPHOTOGRAPHIC EMULSION AND A LAYER CONTAINING METALLIC PHYSICALDEVELOPMENT NUCLEI FORMED IN SITU IN CHLORANIL-MODIFIED GELATIN ISEXPOSED AND DEVELOPED BY A PHYSICAL PHOTOGRAPHIC DEVELOPER.